1. Field of the Invention
This invention relates to motor vehicles.
More particularly, the present invention relates to self-propelled motor vehicles of the type having a pair of laterally spaced steerable wheels for directional control.
In a further and more specific aspect, the instant invention concerns improvements for increasing the directional stability of a motor vehicle, especially during turning or cornering.
2. Prior Art
Turning or cornering is an extremely unstable and inefficient maneuver for a motor vehicle. It is well known that a motor vehicle traveling in a straight line resists turning, in accordance with familiar natural phenomenon, and tends to continue to move in the pre-established direction. Even while traversing a curve, the vehicle exhibits an inherent tendancy to return to a more nearly straight path.
Numerous mechanical intricacies and principles of physics come into play when a motor vehicle is caused to deviate from straight line travel. The contemporary passenger automobile, for example, has a tread dimension, the measurement from center to center of a lateral pair of wheels, of generally between four and five feet. During linear motion of the vehicle, all of the wheels travel substantially the same distance. While traversing a curve, however, the several wheels, four in a conventional passenger automobile, travel differing distances.
Consider, for example, a vehicle having a tread dimension of four and one-half feet and traversing a 90.degree. curve having a nominal radius of forty feet. The inboard wheels, turning upon a radius of thirty-seven and three-fourths feet, travel a distance less than thirty feet. The outboard wheels move through a distance greater than thirty-three feet as a result of the respective radius of forty-two and one-fourth feet.
All of the wheels of a vehicle negotiate a given maneuver within the same time. It is immediately apparent from the foregoing example, therefore, that the outboard wheels must rotate faster than the inboard wheels when a vehicle is turning. Equally obvious is the fact the steerable wheels, usually the front pair, must be set at different steering angles. That is, the inboard wheel must be turned or deflected at a greater angle from normal than the outboard wheel. The rear wheels, not usually having steering capability, do not track or follow the paths of the respective front wheels.
As a result of inertia, kinetic energy of the vehicle, the change of direction is resisted. Even though the steerable wheels are turned at a direction to establish the new course of travel, i.e., traversing a curve, the vehicle has an inherent tendancy to continue in the previous direction. After overcoming the initial resistance of turning, the vehicle is subjected to the effects of centrifugal force which tends to pull the vehicle in a direction away from the apex of the curve. Since the wheels are frictionally adhered to the surface of the road, centrifugal force has the effect of inducing tilt into the body of the vehicle.
The foregoing mechanical and physical factors are responsible for the instability of a motor vehicle while traversing a curve and the inefficiency of the maneuver. In a corner smartly taken, i.e., within limits of relative safety, neither reckless nor dawdling, the vehicle is caused to lean or tilt to the outside of the curve. The average passenger automobile will deflect approximately one and one-half inches such that a given point on the inboard side of the vehicle will be approximately three inches above the corresponding point on the outboard side.
The lean of the vehicle transfers weight from the inboard wheels to the outboard wheels. In the above described cornering maneuver, the weight on the outboard wheels will be approximately twice the weight on the inboard wheels. In other words, two-thirds of the weight of the vehicle will be borne by the outboard wheels while only one-third is carried by the inboard wheels.
Traction of the steerable wheels is a primary consideration affecting directional stability of a motor vehicle. The load upon the steerable wheels and the area of contact with the road are major contributors to traction. During cornering, the traction of the inboard steerable wheel is substantially reduced. Under extreme conditions, such as a slippery road surface or hard cornering in which the wheel may be even lifted from the road, the usefulness of the inboard steerable wheel is materially reduced or even negated.
Although under identical conditions the weight upon the outboard steerable wheel is materially increased, the area of contact with the road is not substantially increased. Accordingly, directional stability is greatly impaired. In a condition known as understeer, responding to inertia and centrifugal force, the vehicle tends to "plow" or travel in a straight line rather than turn in proportion to the steering angle of the steerable wheels.
Understeer is intensified in a vehicle having rear driving wheels which function to push the vehicle straight ahead. Front wheel drive vehicles suffer from a condition known as "torque steer", the inherent characteristic to veer laterally in response to acceleration. Accordingly, acceleration while traversing a curve can heighten the already unstable condition.
Front wheel drive vehicles, which are becoming increasingly popular and captivating an even greater share of the market, suffer from another notable shortcoming while cornering. It is well recognized by those in the automotive field that the inboard front wheel is most affected in terms of loss of traction as a result of cornering. It is also well known that conventional differential gearing will supply driving force to one of the pair of driving wheels that offers the least resistance to rotation. Accordingly, depending upon the speed at which the corner is traversed and the adhesion of the road surface, a substantial portion or even all driving force can be lost.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies of the prior art for which solution has not heretofore been provided.
Accordingly, it is an object of the present invention to provide improvements for motor vehicles.
Another object of the invention is the provision of means for increasing the efficiency of a motor vehicle while traversing a curve.
And another object of this invention is to provide means for equalizing traction of the steerable wheels of a motor vehicle.
Still another object of the invention is the provision of an improved vehicle having a modular drive unit.
Yet another object of the immediate invention is to provide a vehicle which is readily serviceable.
Yet still another object of the invention is the provision of a front wheel drive vehicle which is inherently stable.
A further object of the instant invention is to provide means for transferring weight from the outboard steerable wheel to the inboard steerable wheel of a motor vehicle while traversing a curve.
And a further object of the invention is the provision of a motor vehicle which is capable of traversing a corner or curve at a greater rate of speed than contemporary vehicles.
And still a further object of the invention is to provide a vehicle having cornering capabilities such that the rear wheels tend to track with the front wheels.
Yet still a further object of the present invention is the provision of improvements, according to the above, which are relatively simple and economical to institute.